The present invention relates to a method and an apparatus for joining parts to be joined which are subject to tolerance in the aerospace sector.
Modern lightweight construction methods have greatly changed the aerospace sector in the recent past. The use of suitable materials has accordingly led to improvements in terms of weight, safety and comfort, while simultaneously enabling cost savings. In addition to the use of suitable materials, this progress has been achieved by intelligent use of modern adhesives technology, it being possible to combine adhesives technology with conventional joining techniques such as riveting, screw fastening or spot welding.
The fuselage of large aircraft is substantially joined together manually using a semi-monocoque construction method. Using apparatuses of an appropriate size, the fuselage of an aircraft is fitted in partially mechanized and in part in manual assembly steps with stringers, frame elements, passenger and cargo decks, door and window frames, before the skin is completed.
Structurally significant connections are made by riveting or by a combination of riveting and adhesive bonding, the latter also being known as rivet bonding. In this method, both panel and fuselage segments and the introduced components are connected together by riveting, with shim materials being applied prior to joining which fill the slightly uneven gap between the parts to be joined which is left by riveting.
With regard to shim materials, a distinction is drawn between liquid shims and solid shims. Liquid shims generally comprise two-component epoxy resins, which have a gap-filling capacity of approximately 1 mm and a curing time of nine hours at room temperature.
DE 10 2010 010 685 A1 discloses a method for applying adhesive in vehicle construction when joining parts to be joined which are subject to tolerance, characterized by automated determination of the geometric data of the parts to be joined, determination of the joining gap dimensions of the parts to be joined from the determined geometric data, joining of the parts to be joined in their joining position, and application of the adhesive in the joint gap during or after joining of the parts to be joined.
Relatively large gaps from 1-2 mm in size are generally compensated manually by means of solid shims made from fiber composite material. A combination of liquid and solid shim materials may also be used.
There are various kinds of solid shims. On the one hand, solid shims may be made from a sheet material consisting of metal or fiber composite materials. The sheets are of different thicknesses, from which the shims are cut with the contour of the gap to be closed.
Shims in sheet form may moreover already have the subsequent contour and be made in different thicknesses. On the other hand, solid shims may take the form of adhesively bonded layers which are individually peelable for adjusting thickness.
There are moreover shaped shims which are preshaped with a mould into the curved shape which fits the gap to be closed. Depending on the particular gap profile, there are various methods by which the above-described solid shims may be introduced into the gap.
In the case of gaps with a straight or parallel profile, the gap can be filled in with sheet material which has been cut to size. The thickness of the sheet is here determined from the gap which arises, and the shape from the joint face. To this end, the shim is cut or sawn in the appropriate thickness for the surface from a large, previously manufactured sheet which is held in stock in various thicknesses.
The contour of the solid shims may moreover already be conformed to the parts to be joined and held in stock in various thicknesses. This saves the step of cutting to size before the joining process, since all that remains to be done is to insert the appropriate shim for the location to be closed in the thickness to be used for the assembly gap. Such a gap profile may also be filled with adhesively bonded layers in which the thickness may be established by peeling off individual layers.
In the case of gaps with a wedge-shaped profile, the sheet material, irrespective of whether the contour is cut from a sheet or is already held in stock with the correct contour, must additionally be ground to the correct wedge shape. In the case of adhesively bonded layers, instead of being ground, the individual layers may be removed in steps in order to obtain the correct wedge shape.
If, in addition to the above-described wedge shape, the part to be joined has a three-dimensional shape, the sheets must additionally be cut to size in such a manner that they can conform in the correct thickness to the shape of the part to be joined. In addition, the wedge shape must be achieved either by grinding or by very fine subdivision into numerous sheets of different thicknesses. Adhesively bonded layers must also be cut to size in such a manner that they can individually conform to the contour without individual layers becoming detached as a result of buckling due to excessive curvature. Again, the wedge shape may be achieved by stepped removal.
A further possibility for reproducing the curved shape is to produce a shim with the correct shape specifically for a possible gap. A mould which has the shape of the subsequent gap is required for this purpose. The shim to be inserted may then be produced in this mould. The shim need only then be adapted to the ultimate shape of the gap, specifically by being ground to the wedge shape.
As described above, filling gaps of curved and wedge-shaped profile with a solid shim can only be achieved with very great difficulty, this being the most problematic application. However, since this is specified from a certain gap dimension, the effort must be made if the components are to be assembled. This effort may take two different forms, depending on which of the above-described methods is used.
If sheet material is fitted into the gap, cutting the sheets to size and grinding them involve considerable individual effort, as these tasks have to be performed anew for each gap. If the curved shape of the gap is filled by a shim which has already previously been produced in a specific apparatus and then held in stock, this entails very considerable logistical effort, high warehousing costs and additional manual labor due to the final adaptation to the wedge shape.